The present invention relates to a high-frequency communication apparatus and, more specifically, to a high-frequency communication apparatus comprising high-frequency circuit elements capable of processing signals of frequencies in a microwave frequency band or a millimeter wave frequency band, and a case containing those high-frequency circuit elements, and a method of manufacturing the high-frequency communication apparatus.
Multifunctional circuit elements have been developed for the miniaturization and cost reduction of automotive radar units using a millimeter wave or high-frequency communication apparatuses and radio terminals using radio waves of frequencies in a frequency band of 300 MHz or above. Those communication apparatuses are formed by containing a single multifunctional semiconductor device, a semiconductor integrated circuit (IC), an IC package formed by packaging an IC, a plurality of interconnected ICs or a high-frequency circuit element having a filtering function in a case. A transmitter-receiver for an automotive radar unit disclosed in xe2x80x9c60 GHz Band Millimeter Wave Radar Unit:, 1997 Denshi Joho Tsushin Gakkai Sogo Taikai, C-2-121 is an example of such a communication apparatus. This radar unit has a transmitter-receiver circuit which receives and transmits millimeter wave signals (signals of frequencies in a 60 GHz band) contained in a case having flat surfaces. A RF subsystem shown in a catalog xe2x80x9cRF, Microwave and Millimeter Wave, Single and Multi-Function Components and subassembliesxe2x80x9d of M/A-COM, USA, 1996 is another example of such a communication apparatus. This RF subsystem has a plurality of RF functional circuit elements contained in a case. The internal space of the case is divided into a plurality of sections by metallic walls to reduce adverse effects due to interference between the functional circuit elements.
When packing a plurality of functional circuit elements in one case, the physical distances between the functional circuit elements decreases as the number of the functional circuit elements increases when the size of the case is fixed or the size of the case is large as compared with half the free-space wavelength at a signal frequency, such as about 1.95 mm at 77 GHz. In either case, radio wave energy of a signal frequency radiated from one point on an IC or the like included in a functional circuit element placed in the case are able to propagate easily in the case and causes various functional troubles in other functional circuit elements packed in the same case. For example, in a communication transmitter-receiver and a transmitter-receiver module for an automotive millimeter wave radar unit, part of a signal radiated into a case by a transmitting functional circuit element affects the function of a receiving functional circuit element and causes troubles including the saturation of a receiver and increase in the noise level of received signals.
To prevent such troubles in a case that may be caused by interference between signals in the case, the inner space of the case of a conventional communication apparatus is divided into a plurality of small rooms by metallic walls or a metallic structure that functions as a local cutoff waveguide for cutting off unnecessary radiation is disposed on a signal passage. These prior art techniques need a complicated metallic structure in the case, need a high-frequency wiring board of a passive circuit to be divided into a plurality of parts. These structures and the division of the wiring board into a plurality of parts make the arrangement of semiconductor ICs and passive circuit components difficult, which has been an impediment to the mass production and cost reduction of the communication apparatus.
The applicant of the present patent application has previously filed patent applications: Japanese Patent Laid-open No. Hei 11-118047 (U.S. Patent Application No. 09/557,827 (filed Apr. 25, 2000), Eur. Pat. App. No. 00108878.0 (filed Apr. 26, 2000) to propose means for solving the foregoing problems.
The present invention relates to improvements in the previous proposals and it is an object of the present invention to control impediments to the mass production and/or the cost reduction of communication apparatuses and to provide a high-frequency communication apparatus capable of suppressing interference between electromagnetic waves inside and outside a case, i.e., undesired electromagnetic coupling of circuit elements packed in a case or undesired coupling of circuit elements packed in a case and electromagnetic waves prevailing outside the case.
With the foregoing object in view, the present invention provides a high-frequency communication apparatus comprises high-frequency circuit elements which deal with signals of a frequency in a high-frequency band, such as microwave signals or millimeter wave signals, antenna, and a case containing at least the high-frequency circuit elements; wherein projections are formed in a pattern by press working at least in part of walls forming the case. The part provided with the projections of the walls of the case serves as a filter that attenuates signals of frequencies in a frequency band including the frequencies of unnecessary radio waves that cause troubles in the case.
The high-frequency communication apparatus of the present invention is capable of preventing radiation energy radiated by unnecessary radio wave radiating sources placed in the case from adversely affecting other circuit elements packed in the case by confining the radiation energy in local regions and of radiation energy radiated by unnecessary external radio wave radiating sources from interfering with the operation of the circuit elements packed in the case by attenuating the radiation energy. If radio waves of different frequencies that cause troubles exist in the case, a plurality of kinds of problems attributable to the interference of those radio waves in the operation of the circuit elements can be dealt with by forming projections in patterns on proper parts of the walls of the case. When projections are formed in a pattern on the top wall of the case and the top wall is used as a cover, the case can be formed in a simple shape, such as the shape of a rectangular solid, of a size far greater than the wavelength, a single large high-frequency wiring board can be used, semiconductor devices can be easily disposed in the case, and a module including the case can be manufactured at a low cost.